Question

The figure shows a coral reef deposit at the continental margin since 120 Ma. Assuming that there was no sea-level change, the average subsidence rate of this continental margin is ......... mm/year. (Round off to three decimal places)

Hint:

To calculate the subsidence rate, divide the total subsidence (in meters) by the time (in years) and then convert from meters to millimeters by multiplying by 1000.

Answer 1

Correct Answer: 25

Given:
- Total subsidence = 3000 m (the height of the coral reef deposit)
- Time = 120 Ma = \( 120 \times 10^6 \, \text{years} \)
Step 1: The formula for subsidence rate is:
\[ \text{Subsidence rate} = \frac{\text{Total subsidence}}{\text{Time}} \]

Step 2: Substitute the values into the formula:
\[ \text{Subsidence rate} = \frac{3000 \, \text{m}}{120 \times 10^6 \, \text{years}} \]

Step 3: Simplify the calculation:
\[ \text{Subsidence rate} = \frac{3000}{120 \times 10^6} = 0.025 \, \text{m/year} \]

Step 4: Convert to mm/year:
\[ 0.025 \, \text{m/year} = 25 \, \text{mm/year} \]
Thus, the average subsidence rate is 25 mm/year.
\[ \boxed{25 \, \text{mm/year}} \]